1. Field of the Invention
This invention relates to a process for the production of oligomeric fatty acids and lower alkyl esters thereof by oligomerization of fatty acids or lower alkyl esters thereof in the presence of Lewis acids.
2. Statement of Related Art
Oligomeric fatty acids and their esters, i.e. technical mixtures of acyclic and cyclic di-, tri- and oligocarboxylic acids or esters, are important products which are used for the production of adhesives, paints, fibers, corrosion inhibitors and lubricants.
Among the oligomeric fatty acids, the dimer fatty acids are particularly important. They are normally obtained by oligomerization of unsaturated fatty acids at temperatures of 180.degree. to 250.degree. C. in the presence of aluminas, for example montmorillonites (Fette, Seifen, Anstrichmittel, 72, 667 (1970)). However, the process is attended by the disadvantage that achieving satisfactory oligomerization yields requires not only comparatively high catalyst concentrations, but also drastic reaction conditions which involve high energy consumption.
It is known from Rev. Fr. Corps. Gras, 33, 431 (1986) that the oligomerization of linoleic acid can also be carried out in the presence of ruthenium or nickel on active carbon supports. Although the process manages with low catalyst concentrations, high yields of oligomers are only obtained at temperatures above 200.degree. C.
Finally, it is reported in Fette, Seifen, Anstrichmittel, S80, 186 (1978) that linoleic acid esters can be quantitatively oligomerized at only 80.degree. C. in the presence of rhodium/olefin complexes and tin(II) chloride. This process has the disadvantage that the production of rhodium/olefin complexes involves significant outlay on equipment. In addition, the use of homogeneous rhodium catalysts is economically unfavorable.